The present invention relates generally to spectrophotometers, which are optical instruments that measure the amount of light transmitted or reflected by a sample as a function of the wavelength of the light. Radiometers, on the other hand, measure the radiation emitted by a source, with no intervening sample.
While the optical configuration of a spectrophotometer can take many forms, all current spectrophotometers have one property in common--serial scanning of wavelength. This function is carried out in the monochromator portion of the spectrophotometer, which separates light into various wavelengths. The monochromator may be used prior to sample illumination, in which case the sample is illuminated with monochromatic light. If the monochromator is placed after the sample, the sample is illuminated with polychromatic light. This latter configuration is preferable when sample fluorescence is to be excited and measured.
The means by which the light is divided into its component wavelengths in the monochromator can include dispersive elements such as diffraction gratings and prisms, or absorptive elements such as interference filters. Division of the light into its component wavelengths is achieved in a serial or sequential fashion, whereby measurements of transmittance or reflectance are made one wavelength at a time. In certain applications this serial monochromator operation takes too much time to be of practical utility, for example, when the sample is moving so that it is available for measurement only for a short period of time. The measurement of such moving samples is required in many industrial process control applications. The ability to make rapid spectrophotometric measurements could be of considerable value in these areas.
The present invention relates to a new type of spectrophotometer that measures sample transmittance or reflectance at multiple wavelengths simultaneously. The spectrophotometer of the present invention illuminates a sample with flux derived from a light source, such as a pulsed xenon flashtube, divides the light reflected or transmitted by the sample into its component wavelengths and simultaneously senses the energy present in each of the component wavelengths. Thus, spectrophotometric measurements can be made rapidly, since there is no need to sequentially scan through different wavelengths. In addition, the spectrophotometers of the present invention need no moving parts.